Re: [CHECKER] copy_*_user length bugs?
Chris Evans <[EMAIL PROTECTED]> writes: |> To justify this, consider if len were set to minus 2 billion. This will |> pass the sanity check, and pass the value straight on to copy_to_user. The |> copy_to_user parameter is unsigned, so this value because approximately |> +2Gb. |> |> Now, providing the malicious user passes a low user space pointer (e.g. |> just above 0), the kernel's virtual address space wrap check will not |> trigger because ~0 + ~2Gb does not exceed 4G. And the result is the user |> being able to read kernel memory. On m68k this is not a problem, since kernel and user address space are strictly distinct, even in the kernel. The luser will get an EFAULT eventually. Andreas. -- Andreas Schwab "And now for something SuSE Labscompletely different." [EMAIL PROTECTED] SuSE GmbH, Schanzäckerstr. 10, D-90443 Nürnberg Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [CHECKER] copy_*_user length bugs?
On Wed, 18 Apr 2001, Russell King wrote: > > Now, providing the malicious user passes a low user space pointer (e.g. > > just above 0), the kernel's virtual address space wrap check will not > > trigger because ~0 + ~2Gb does not exceed 4G. And the result is the user > > being able to read kernel memory. > > But ~0 + ~2GB = ~2GB. Last time I checked, ~2GB is less than 3GB, and 3GB > is the start of kernel memory on x86. Therefore, I don't see that the > user will be able to read kernel memory. The problem is that (up to) a 2Gb copy is attempted into userspace. The source is a kernel object which is not 2Gb large! So, we read off the end of some kernel object, and there is often something very interesting after it ;-) For a good real-world example, please see my Bugtraq post regarding sysctl(): http://www.securityfocus.com/archive/1/161764 Cheers Chris - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [CHECKER] copy_*_user length bugs?
On Wed, Apr 18, 2001 at 12:14:56PM +0100, Chris Evans wrote: > To justify this, consider if len were set to minus 2 billion. This will > pass the sanity check, and pass the value straight on to copy_to_user. The > copy_to_user parameter is unsigned, so this value because approximately > +2Gb. For ARM, this isn't a problem (we do 33-bit arithmetic in access_ok specifically to catch this type of thing). x86 does the same thing (or did when I wrote the code for ARM. > Now, providing the malicious user passes a low user space pointer (e.g. > just above 0), the kernel's virtual address space wrap check will not > trigger because ~0 + ~2Gb does not exceed 4G. And the result is the user > being able to read kernel memory. But ~0 + ~2GB = ~2GB. Last time I checked, ~2GB is less than 3GB, and 3GB is the start of kernel memory on x86. Therefore, I don't see that the user will be able to read kernel memory. -- Russell King ([EMAIL PROTECTED])The developer of ARM Linux http://www.arm.linux.org.uk/personal/aboutme.html - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [CHECKER] copy_*_user length bugs?
On Tue, 17 Apr 2001, Dawson Engler wrote: > Hi All, > > at the suggestion of Chris ([EMAIL PROTECTED]) I wrote a simple > checker to warn when the length parameter to copy_*_user was (1) an > integer and (2) not checked < 0. > > As an example, the ipv6 routine rawv6_geticmpfilter gets an integer 'len' > from user space, checks that it is smaller than a struct size and then > uses length as an argument to copy_to_user: > > if (get_user(len, optlen)) > return -EFAULT; > if (len > sizeof(struct icmp6_filter)) > len = sizeof(struct icmp6_filter); > if (put_user(len, optlen)) > return -EFAULT; > if (copy_to_user(optval, &sk->tp_pinfo.tp_raw.filter, len)) > return -EFAULT; > > Is this a real bug? Or is the checked rule only applicable to > __copy_*_user routines rather than copy_*_user routines? (If its a real > bug, theres about 8 others that we found). > > Thanks, > Dawson Length is type size_t (unsigned). It can't be less than zero. copy_to_user() should fault with invalid lengths. That's one of the things it's supposed to do. Cheers, Dick Johnson Penguin : Linux version 2.4.1 on an i686 machine (799.53 BogoMips). "Memory is like gasoline. You use it up when you are running. Of course you get it all back when you reboot..."; Actual explanation obtained from the Micro$oft help desk. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [CHECKER] copy_*_user length bugs?
On Wed, 18 Apr 2001, David Schleef wrote: > On Tue, Apr 17, 2001 at 09:39:15PM -0700, Dawson Engler wrote: > > Hi All, > > > > at the suggestion of Chris ([EMAIL PROTECTED]) I wrote a simple > > checker to warn when the length parameter to copy_*_user was (1) an > > integer and (2) not checked < 0. > > > > As an example, the ipv6 routine rawv6_geticmpfilter gets an integer 'len' > > from user space, checks that it is smaller than a struct size and then > > uses length as an argument to copy_to_user: > > > > if (get_user(len, optlen)) > > return -EFAULT; > > if (len > sizeof(struct icmp6_filter)) > > len = sizeof(struct icmp6_filter); > > if (put_user(len, optlen)) > > return -EFAULT; > > if (copy_to_user(optval, &sk->tp_pinfo.tp_raw.filter, len)) > > return -EFAULT; > > > > Is this a real bug? Or is the checked rule only applicable to > > __copy_*_user routines rather than copy_*_user routines? (If its a real > > bug, theres about 8 others that we found). > > The len parameter is an unsigned value, so this code is ok as > long as access_ok() correctly checks that the range to copy > doesn't stray outside of the userspace range, including the > possible wraparound for a very large len. access_ok() on i386 > checks for the wraparound. m68k doesn't use it. PowerPC > is correct, but only because TASK_SIZE is 0x8000. If it > is ever changed, there could be a problem. I didn't check > other architectures, because I don't understand the asm. Incorrect - if the "len" variable is a signed integer, this is a nasty bug. To justify this, consider if len were set to minus 2 billion. This will pass the sanity check, and pass the value straight on to copy_to_user. The copy_to_user parameter is unsigned, so this value because approximately +2Gb. Now, providing the malicious user passes a low user space pointer (e.g. just above 0), the kernel's virtual address space wrap check will not trigger because ~0 + ~2Gb does not exceed 4G. And the result is the user being able to read kernel memory. Cheers Chris - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [CHECKER] copy_*_user length bugs?
On Tue, Apr 17, 2001 at 09:39:15PM -0700, Dawson Engler wrote: > Hi All, > > at the suggestion of Chris ([EMAIL PROTECTED]) I wrote a simple > checker to warn when the length parameter to copy_*_user was (1) an > integer and (2) not checked < 0. > > As an example, the ipv6 routine rawv6_geticmpfilter gets an integer 'len' > from user space, checks that it is smaller than a struct size and then > uses length as an argument to copy_to_user: > > if (get_user(len, optlen)) > return -EFAULT; > if (len > sizeof(struct icmp6_filter)) > len = sizeof(struct icmp6_filter); > if (put_user(len, optlen)) > return -EFAULT; > if (copy_to_user(optval, &sk->tp_pinfo.tp_raw.filter, len)) > return -EFAULT; > > Is this a real bug? Or is the checked rule only applicable to > __copy_*_user routines rather than copy_*_user routines? (If its a real > bug, theres about 8 others that we found). The len parameter is an unsigned value, so this code is ok as long as access_ok() correctly checks that the range to copy doesn't stray outside of the userspace range, including the possible wraparound for a very large len. access_ok() on i386 checks for the wraparound. m68k doesn't use it. PowerPC is correct, but only because TASK_SIZE is 0x8000. If it is ever changed, there could be a problem. I didn't check other architectures, because I don't understand the asm. dave... - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[CHECKER] copy_*_user length bugs?
Hi All, at the suggestion of Chris ([EMAIL PROTECTED]) I wrote a simple checker to warn when the length parameter to copy_*_user was (1) an integer and (2) not checked < 0. As an example, the ipv6 routine rawv6_geticmpfilter gets an integer 'len' from user space, checks that it is smaller than a struct size and then uses length as an argument to copy_to_user: if (get_user(len, optlen)) return -EFAULT; if (len > sizeof(struct icmp6_filter)) len = sizeof(struct icmp6_filter); if (put_user(len, optlen)) return -EFAULT; if (copy_to_user(optval, &sk->tp_pinfo.tp_raw.filter, len)) return -EFAULT; Is this a real bug? Or is the checked rule only applicable to __copy_*_user routines rather than copy_*_user routines? (If its a real bug, theres about 8 others that we found). Thanks, Dawson - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/